Handle no layers case

lib/cartodb/models/mapconfig_named_layers_adapter.js

@@ -11,6 +11,10 @@ module.exports = MapConfigNamedLayersAdapter;
 MapConfigNamedLayersAdapter.prototype.getLayers = function(username, layers, dbMetadata, callback) {
     var self = this;
 
+    if (!layers) {
+        return callback(null);
+    }
+
     var adaptLayersQueue = queue(layers.length);
 
     function adaptLayer(layer, done) {

lib/cartodb/server.js

@@ -219,7 +219,9 @@ module.exports = function(serverOptions) {
                         return callback(err);
                     }
 
-                    requestMapConfig.layers = layers;
+                    if (layers) {
+                        requestMapConfig.layers = layers;
+                    }
                     return callback(null, requestMapConfig, datasource);
                 }
             );